This invention relates to balloon catheters and relates particularly to the employment of multiple materials and overlay construction in a catheter balloon unit for both improving and tailoring of the characteristics of the balloon unit.
Balloons in a balloon catheter are employed in a patient's body canal, commonly a blood vessel, primarily for three purposes: occlusion, distension (e.g., angioplasty) and vessel cleaning or removal of clots and foreign substances (e.g., embolectomy, thrombectomy). For serving the first purpose, the balloon must be supple enough when inflated to conform completely to the interior surface of the body canal and the surface must have an adequate frictional characteristic to hold the balloon in place. For the second purpose, the balloon must be stiff enough to inflate symmetrically even while being influenced by asymmetric forces. And for the third purpose, the surface must be tear resistant, with good tensile properties, and again must have an appropriate frictional characteristic. Especially because both surface and structural characteristics, such as strength, rigidity and tear resistance, are important, a balloon comprising a single material generally requires the acceptance of trade-offs in the characteristics of the material. Even in view of this, there appear to be few attempts to employ multiple materials in a balloon in an effort to minimize trade-offs so as to optimize desirable characteristics. One reference, Wang, et al., U.S. Pat. No. 5,195,969 ("Wang"), proposes "CO-EXTRUDED MEDICAL BALLOONS AND CATHETER USING SUCH BALLOONS" comprising a multi-layered balloon including a base structural layer of relatively thick ethylenic polymeric material and a second layer co-extruded and apparently bonded co-extensively with the base layer, the second layer preferably being a polyolefin such as polyethylene.
However, even a multiple material balloon such as that proposed by Wang has disadvantages. For example, it is often desired that the balloon present a non-convoluted surface to the interior of the body canal when the balloon is deflated, to facilitate passing the balloon therethrough. If a strong base material is co-extruded with, for example, a soft surface material, the base material is often insufficiently elastic for relaxing to a smooth surface configuration when the balloon is deflated. Moreover, deflation and complete collapse of the balloon, which is resisted by employing a stiff, strong base material, is not aided appreciably by employing a soft co-extruded surface layer.
Accordingly, there is a need for a novel balloon catheter and method for use thereof that employs multiple materials and provides an overlaid construction for optimizing both the surface and structural characteristics of a balloon unit.